Traditional probe card analyzers measure probe planarity by electrical means, and generally measure probe alignment by optical means. Electrical planarity measurements are typically made by slowly bringing a conductive contact surface into contact with the probes on a probe card. In that regard, the conductive contact surface is moved toward the probe card; the conductive surface first makes contact with the probe that extends furthest from the probe card surface (the “lowest” probe), and finally makes contact with the probe that extends least from the probe card surface (the “highest” probe). In this context, the terms “lowest” and “highest” are not necessarily intended to imply a vertical orientation. The process of moving the conductive contact surface from first to last contact point and beyond is generally referred to in the art as “overtravel,” since the first probe to make contact with the conductive contact surface is loaded beyond the point of first contact.
As probes are “overtraveled,” the contact loads increase. For probe cards implementing many probes, these contact loads can become quite high, and are capable of producing deflections in system components that may significantly impact the accuracy of measurement results.
In a typical probe card analyzer system taking electrical planarity measurements across a single large contact surface, the deflection of the probe card, the probe card fixture, the metrology frame, or some combination thereof, may become an integral part of the planarity measurement itself. This is due to the fact that the loads arising from contact with lower probes cause deflection, which in turn increases the apparent planarity of higher probes.
Optical planarity measurements, on the other hand, may be made by optically scanning the tips of free-hanging probes. Under such conditions (i.e., free-hanging probes with no overtravel), contact loads are never created, and hence cannot cause component deflections or flexure of any kind. Accordingly, such optical planarity measurements may differ from electrical planarity measurements, even with respect to the same probe card under analysis. Additionally, optical methodologies generally enjoy a speed advantage over electrical planarity evaluative methods. The rapidity of optical planarity measurements and techniques make such optical technology attractive; it is highly desirable to develop a method of producing equivalent electrical planarity analysis based upon or benefiting from fast optical measurements.
Currently implemented systems and methods are deficient in that traditional methodologies do not accurately correlate optical planarity measurements, which are made in the absence of contact loads, to electrical planarity measurements, which are made in the presence of, and are influenced by, such contact loads.